A power supply is integrated into nearly every electronic device, both consumer and industrial, including vehicle powertrain electronics, portable electronic equipment, integrated in-vehicle systems, computers, medical instrumentation, and many other devices. Within an electronic device, it may be necessary to either increase or decrease a voltage by using either a step-up or a step-down power converter (called a buck or boost). A step-up, or boost, converter can be used to increase voltage, and a step-down, or buck, converter can be used to decrease voltage.
Short circuits of the output voltage node, however, can cause the power converter assembly not to operate properly. Thus, short circuit to ground solutions have been implemented by those of skill in the art.
In certain conditions, however, the output voltage node may be shorted to a different voltage rail, or a non-ground, which is higher than the output voltage and lower than the input voltage and nevertheless can cause a rise of the input voltage node. This can damage electronics connected to the input voltage node and/or the MOSFETs or other switches used in the converter. For example, in a synchronous buck regulator, the catch diode is replaced by a low-side switch, the control of which is complimentary to the high-side switch. Since, unlike the diode, the low-side switch when turned on can conduct current in both directions, it needs to be protected in case of the output short circuit to a voltage rail. This type of failure will cause reverse current into the buck regulator output, which is only limited by the DC resistance of the buck inductor. At some point the over-current protection of the low side switch will turn it off and the current will start to decay. If this process will repeat over and over, the low-side switch together with the buck inductor, body diode of the high-side switch, and the input capacitor will create a boost topology that will transfer energy from the output to the input. If the pre-regulator stage feeding the synchronous buck regulator can only source current and does not have enough loading, then the voltage at the input capacitor will build up to possibly unsafe higher levels.
Accordingly, there is a need for a low-cost and easily implemented solution for a synchronous buck converter assembly that is capable of effectively protecting against a short circuit to an outside voltage source.